Field of the Invention
The present invention relates generally to seismology. More specifically, the present invention relates to embodiments for forming a seismic trace responsive to seismic signals received at seismic sensors.
Description of the Related Art
Hydrocarbon deposits are often trapped thousands of feet below the Earth's surface. The exploration for such hydrocarbons, particularly with respect to the discovery and analysis of subterranean petroleum deposits, typically employs seismology techniques for imaging the geological structure of the Earth's subsurface. For example, seismic energy waves from an energy source are propagated through the Earth's subsurface and are at least partially reflected through the Earth's subsurface upon being propagated through various forms of subterranean matter having divergent impedances. Particularly, when a seismic energy wave encounters a boundary between two different materials with different impedances, at least some of the energy will be reflected off the boundary. The reflected seismic energy can then be received at predetermined locations, such as on land, within the sea, or in boreholes using strategically positioned sensors to receive the seismic energy as a signal and to collect and to record data concerning the received seismic energy. The recorded data, which may include properties such as the arrival time and the magnitude of the reflected energy, can be processed to determine the depth and physical properties of the reflecting geological structure. For example, changes in signal properties allow inferences regarding changes in seismic impedances, which thereby allow inferences regarding the properties of the underlying geologic structure, such as the density and elastic modulus of the subsurface matter.
Generally, seismic imaging requires directing an intense sound from a seismic energy source device into the ground to evaluate subsurface conditions and to detect possible concentrations of oil, gas, and other subsurface minerals. Seismic sensor devices, known as geophones, record sound wave echoes that come back up through the ground to the recording surface. Such seismic sensor devices, or geophones, can record the intensity of such sound waves and the time it took for the sound wave to travel from the sound source device back to the geophone recording device at the recording surface. The reflections of sound waves emitted by the sound source device, and recorded by the geophone recording device, can be processed by a computer to generate a three-dimensional digital model, or seismic image, of the subsurface. The three-dimensional model of the subsurface can be used to identify, for example, the placement of reservoirs and potential well flow paths.
The recorded data is processed, and then the results are used to map the Earth's subsurface structure, such as the structure of rock formations, producing a graphical model of the structure and physical properties of the Earth's subsurface. The results obtained are usually not unique, meaning that more than one model can be found to adequately fit the data. Therefore, a paramount consideration in seismology is to measure the reflected energy in a way that most accurately and completely captures the true geologic subsurface properties of the Earth, and to then extract from those measurements as much information as possible to accurately and completely represent the true geologic structure.
Conventional seismic acquisition systems use an array of strategically positioned seismic sensors; the array is also called a receiver and is typically composed of between 6 and 24 sensors. The sensors in the receiver measure the reflected seismic energy to form the seismic response. The acquisition system collects data corresponding to the measured reflected energy of the receiver, then sums the data for a particular time (t) to produce a seismic response associated with the receiver, which is also known as a seismic trace. Conventional seismic imaging systems may perform the summation using hardwired logic so that all wave fronts recorded by the sensors at a time (t) are directly summed irrespective of the data quality or any potential sensor malfunction. Although hardwired summation may prove efficient in terms of acquisition speed and turnaround time, this method is susceptible to errors and inaccuracies that can cause an inaccurate and incomplete depiction the true geological structure of the subsurface.
Common errors and inaccuracies include, for example, noise leakage due to aliasing, improper summation due to malfunctioning sensors, the introduction of non-geologic seismic effects, source and receiver variation, coherent noises, and electrical noise or spikes. Conventional systems can provide correction functions, which are more commonly adopted today, filter the collected data for noise and aliased data, correct for actual or potential sensor malfunctions, and correct for any non-geologic seismic effects before summing the seismic sensors to produce the seismic trace.